Control system



June 10,1941. J. w. COOKE CONTBQfl SYSTEM Fi-i'ed Dec. 16, i939 2 Sheets-Sheet 1 Inventor: JamesW Cooke, b a/MQ' His Attorney.

June 10, 1941.

J. w. coolq: 2,245,253 CONTROL SYSTEM Filed Dec. 16,1 1959- 2 Sheets-Sheet 2 Fig.2.

Inventor: James W. Co ke, b His Attorney.

Patented June It), 1941 UNITE STAT ES er EN l? rrice CQNTRQL SYSTEM James W. Cooke, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York 8 Claims.

This invention relates to control systems, more particularly to systems for controlling the operation of electric motors, and it has for an object the provision of a simple, reliable, and improved control system of this character.

More specifically, the invention relates to control systems in which a shunting circuit for the motor is established to provide a creeping speed for the motor and in which a solenoid brake having its solenoid connected in circuit with the motor is provided for braking the motor to rest, and in which means such as a limit switch are provided for disconnecting the motor from its source, and a further object of the invention is the provision of means for overcoming certain objectionable operating features which are encountered in control systems of this character.

For example, a series wound direct current motor has certain very desirable operating characteristics when used for crane hoist work. In order to obtain good speed regulation under varying loads, it is customary to provide a shunting connection for the motor on one or more low speed points of the master switch. It is possible to obtain this shunt connection by leaving closed on the low speed points of the master switch, a spring closed contactor which is used for emergency dynamic braking. This permits fairly stable creeping speeds to be obtained without having to add any additional devices to the control.

However, this shunt connection introduces an undesirable operating condition in that it establishes a bypass or sneak circuit around the motor armature and series field. This sneak circuit will keep the series brake released even though the limit switch has operated to disconnect the hoist motor from its source. Under this condition, if the load on the hook is surficient to overhaul the motor, the load will descend to the point at which the limit switch resets itself and will then start up again. Thus an oscillating or hunting action of the crane hook is set up which will continue until the operator returns the master switch handle back to its off position or to a position on the hoisting side on which the motor shunting connection is removed, and the brake will set and stop the load when the limit switch trips.

It is rather disconcerting to an operator to have a control on a crane which will allow the load to stop hoisting and start to descend even though the master switch handle remains in one of its hoisting positions. If there is a very heavy load on the crane when this tripping action occurs, the load will drop quite suddenly through the distance required for resetting the limit switch, thus subjecting the entire hoist mechanism to rather high and unnecessary strains.

A power type limit switch is considered as an emergency overtravel protective device and should not be called upon to operate more often than necessary since its dependability in case of an emergency will be increased if it is not subjected to unnecessary wear and tear caused by a large number of unncessary operations. A"- cordingly, a more specific object of this invention is the provision of means for eliminating this oscillating action of the crane hook, while still maintaining the creeping speed shunting connection for all normal operation of the control.

A large percentage of cranes incorporate a trolley structure on which the hoist mechanism, including hoist motor and solenoid brake, is mounted. The main magnetic control panel or manual drum switch is usually located on the bridge, and it is necessary to make the power connections between the motor and the brake and the panel by means of trolley wires and collector shoes. Heretofore a control system has been used in which four electrically independent trolleys and sets of shoes were rquired. Trolley wires on a crane are not only expensive to install but they take up space and are also a potential source of trouble and require constant maintenance and inspection to keep them in proper condition. Accordingly, a further object of this. invention is the provision of means for eliminating the undesirable operating conditions described in the foregoing without increasing the number of trolley wires.

In carrying the invention into effect in one form thereof, means are provided establishing a shunting circuit for the motor to provide the desired stable creeping speed, and a brake is provided for the motor having its operating coil in series with the motor. Means responsive to operation of the motor are provided for disconnecting the motor from the supply source without interrupting the shunting circuit through which the solenoid oi the brake remains connected to the source and the brake released. In addition, however, means responsive to the disconnection of the motor from the source are provided for interrupting the shunt circuit to effect deenergization of the solenoid and setting of the brake. Means may also be provided which establish a dynamic braking circuit for the motor in response to this disconnection of the motor -in circuit with motor I2.

from its source to assist the solenoid brake in bringing the motor and its load to rest in the event that the load is overhauling.

In illustrating the invention in one form thereof, it is shown as embodied in a control system for crane hoists and the like.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawings of which Fig. 1 is a simple diagrammatical sketch of the master switch and control circuits controlled thereby, Fig. 2 is a simple diagrammatical sketch of the power circuits and of the contacts therein controlledby the control of Fig. 1, and Fig. 3 is a simple diagrammatical sketch of the crane hoist cable and limit switch operated thereby.

Referring now to the drawings, the hook Iii of a crane hoist is connected to a cable II which is wound upon a drum II', or unwound therefrom, by means of a motor I2. This hoist motor is illustrated as a series type direct current motor, having a series field winding I2a, and a commutating field winding IZb. The motor may be supplied from any suitable source such as represented by the two supply lines I3 and I4.

A pair of reversing contactors I5 and I6 are provided for connecting the motor to the source for rotation in opposite directions. These contactors have operating coils I51 and Ifis, respectively, as shown in Fig. 2. These operating coils are also shown including their controlling circuits in Fig. 1. When contactor I5 is closed, motor i2 is connected to source I3, Hi for rotation in the lowering direction, and when contactor E is closed, the motor is connected to the source for rotation in the hoisting direction.

Referring to Fig. 1, the operating coils I5a and Ifia of the contactors are under the control of a multiposition, reversing type master switch i 1. The master switch I! is illustrated as having five Hoisting positions and five Lowering positions. A greater or lesser number of operating positions might be provided if desired.

Hoist motor I2 is provided with a solenoid brake (not shown) having its operating solenoid it connected in series with the motor series field through resistors I9, 20, and 2| and 22. Resistors I9, 20 and 2| are active during the lowering operation, but are short circuited in all positions of the master switch during the hoisting operation.

A normally spring closed contactor 23 serves to establish a shunting connection for motor I2 through a resistor 24 in certain slow speed positions of the master switch in order to provide the desired slow creeping speeds. Contactor 23 is provided with a coil 23:; which when energized serves to open the contactor against the tension of its closing spring (not shown). The control circuits for operating coil 232. are shown in Fig. 1.

Accelerating resistors 25 and 26 are connected controlled by means of accelerating contactors 21 and 28 having operating coils 21a, and 282., respectively. The control circuits for the operating coils 27a and 28a are shown in Fig. 1.

An overhoist limit switch 29 is provided for disconnecting the motor I2 from the source at a predetermined position of the hook in order to prevent overtravel in the hoisting direction. This limit switch is illustrated in Fig. 3 as a plurality .of pairs of stationary contacts 29a, 29b, 29, 29d, and a cooperating movable contact member 29e- These resistors are A projecting member 30 secured to the cable I I serves to actuate the movable member 2%. The contacts 295. and 29b are normally closed and contacts 296 and 29d are normally open except when the hook reaches its overhoist limit and the member 30 actuates the movable member to open contacts 29a and 29b and to close contacts 290 and 29a.

The hoist motor I2, series brake l8, and limit switch 29 are mounted on th trolley structure, and the various resistors and contactors described in the foregoing are mounted on a main magnetic control panel which is usually located on the bridge. Thus it becomes necessary to make the power connections between the motor and the brake and the panel by means of trolley wires and collector shoes. These trolley wires are indicated by reference characters 3!, 32, 33, and 34.

For the purpose of deenergizing the solenoid of Series brake I8 when the limit switch 29 disconnects motor I2 from the source, a relay 35 is provided. The operating coil 359. of this relay is connected between trolley wire 32 and the common point of resistors 24 and 25. The contacts 35b of this relay are connected in circuit with the operating coil 23a of contactor 23 when the hoist contactor I6 is closed as shown in Fig. 1;

With the foregoing understanding of the elements and their organization in the control system, the operation of the system itself will readily be understood from the following detailed description.

It is assumed that the hook is in its lower position and that the master switch I1 is in its central or ofi position. The apparatus will all be in the normal position in which it is shown in the drawings, and the hoist motor I2 will be at standstill, and the series brake set. In the off position of the master switch a dynamic braking circuit is established which is traced from the right-hand armature terminal through limit switch contact 23b, coil 35a, resistor 24, normally closed contacts of contactor 23, series field winding I2a, limit switch contacts 29a. to the left-hand terminal of motor I2. Also, in the OE position of the master switch, the operating coils 35a, 31a and 38a of contactors 36, 31 and 38, respectively, are energized. The circuit for coils 36a and 31a. is traced from the side 39 of a suitable source of control voltage, through conductor 49, fingers '12. of master switch I1, bridged by segment I'lb, operating coils 36a. and 318. in parallel to the opposite side GI of the source of control voltage. In this connection, it will be noted that contacts 68b of control relay 60 are closed, and that the circuit for coil 35a is completed when contacts 31b of contactor 31 close. The circuit for coil 38a. is traced from conductor 40 through fingers ment Ila, coil 38a to the side 4| of the source.

As a result contactors 36, 37 and 38 are closed, and resistors I9, 20 and 2I are short circuited.

To hoist the hook and its loadythe master switch is operated to its first position Hoist. In this position the coil 42a of disconnect contactor $2 is energized. The circuit is traced from the side 39 of source of control voltage to power conductor 40, fingers I16 of master switch bridged by segment I11, conductor 43, coil 42a to the opposite side 4| of the control voltage source. Contactor 42 closes in response to energization and connects one terminal of the motor to the side I4 of the power supply source.

Simultaneously, the operating coil '65, of Hoist lie of the master switch bridged by segcontactor i is energized; the circuit is traced from power conductor 48 through fingers H of the master switch bridged by segment l'lh, normally closed contacts 44b of dynamic braking contactor 46, operating coil of hoist contactor to side 4| of the source. As a result Hoist con.- tactor closes its normally open contacts lBb, Hie and [6a. Contacts Hit, in closing, complete the power circuit for the motor which is traced from the side is of the supply source, through conductor 55, contacts Hit of the Hoist contactor, accelerating resistors 26 and 25, coil 35a of relay 35, limit switch contacts 29b, armature of motor [2, conductor 5%, limit switch contacts 295., series field winding Elia, series brake operating solenoid l8, contacts 35b of contactor 33, conductor 41, resistor 22, contacts 42 of contactor 42 to the side M of the power supply source. The normally open contacts I50 and His of Hoist contactor !B are also closed. The coil 23a, of contactor 23, however, remains unenergized since the circuit for its operating coil is open at the contacts 48a of relay ea. Also the contacts 35b of relay 3'5 are opened in respons to energization of the coil 35a which i connected in series with the motor armature. Consequently, the circuit of coil 23a. is interrupted at two points, and the normally closed spring operated contacts 23b of contactor 23 remain closed and complete a shunting circuit for motor !2 through resistor 24. As a result the motor l2 rotates at a stable slow speed and hoists the load.

In order to increase the speed, the master switch H is actuated to its second position Hoist. In this position, a circuit is completed for the operating coil 4% of accelerating contactor Ml. This circuit is traced from the power conductor 30, through fingers I11 bridged by segment l'i' conductors 5G and 5!, contacts Hid of. the Hoist contactor, operating coil 42a, to the side M of the source. In response to energization, contactor 49 closes its contacts 69b to short circuit accelerating resistor 22. This results in increasing the speed of motor l2.

Movement of the master switch to the third, fourth and fifth positions, Hoist, successively opens the motor shunt through contactor 23, and short circuits accelerating resistors 25 and 25. Since these operations do not constitute any part of the present invention, the control circuits established by the master switch to bring about these operations are not traced or described.

If the master switch should be in either its first or second low speed positions when the hook reaches the overhoist limit, the contacts of contactor 23 will be closed, because the master switch does not open this contactor until the master switch is moved to its third position Hoist or to its ofi position.

As the hook reaches the overhoist limit, the projection 33 strikes movable switch member 29c and moves it from the position shown to the position in which contacts 29a and 29b are open and contacts 29c and 29s are closed. Contacts 29a and 28b, in opening, disconnect motor l2 from the source I3, Hi and disconnect the series field lZa from the motor, and contacts 2% and 29d, in closing, complete a dynamic braking circuit-for the armature of motor l2 which is traced from the right-hand armature terminal of motor l2 through contacts 2%, series field winding 12a, dynamic braking resistor 52, contacts 29 and conductor 46 to the left-hand terminal of the motor armature. As a result of the establishment of this dynamic braking circuit, a large braking torque is set up which is effective in rapidly reducing the speed of the motor. In this connection it will be noted that contacts 290 and 29a reconnect the series field winding to the armature of motor [2 so that the current flows through the series field winding in the same direction as it did during the previous power operation. As a result the current in the series field winding does not decrease to Zero, and the braking torque is therefore maintained at maximum value.

The opening of contacts 2% to disconnect the motor armature from the source also results in deenergizing the operating coil 35a of relay 35. Contacts 35b close in response to deenergization of the operating coil 35a and complete an energizing circuit for the operating coil 23?. of contactor 23. This circuit extends from the power conductor 48 through fingers ilk of the master switch bridged by segment i'h, conductor 53, contacts 35b, conductor 54, contacts I50 of the Hoist contactor (in the closed position thereof), coil 23a of contactor 23 to the side 4| of the source. In response to energization, contactor 23 opens its contacts 23b and interrupts the by-pass circuit to solenoid brake coil l8. As a result the coil i8 is deenergized and the brake shoes are set by their springs (not shown) against the brake drum (not shown) on the shaft of motor i2. Thus, even though the load on the hook be sufiicient to overhaul the motor, the brakewill set and bring the motor and its load quickly to standstill.

It will be noted that if the relay 35 had not energized the operating coil 23a, the contactor 23 would have remained closed and the brake solenoid would have remained energized over the following circuit: from the side l3 of the supply source, conductor 45, contacts Hit of the Hoist contactor, resistors 26, 25, and 24, contacts 23b of contactor 23, brake solenoid l8, contacts 36b, conductors 51 and 41, resistor 22 if master switch i1 is at its first position hoist or contacts 49b of accelerating contactor 455 if master switch is at its second position hoist, contacts 42 of contactor 42 to the side I4 of the source. As a result, the brake would have remained released, and if the load on the hook had been overhauling, it would have started to lower when the limit switch disconnected motor 12 from the supply source, even though the handle of the master switch was in one of its hoist positions. Such an operating condition is undesirable, and has been eliminated by the means described in the foregoing.

By returning the master switch H to its ofi position, the circuit for the operating coil 23g. of contactor 23 is interrupted at the fingers llk of the master switch. Simultaneously, the Hoist contactor it is opened. Thus with limit switch 29 in its tripped position, the hoist motor cannot be energized or the brake released if the master switch is again actuated to one of its hoisting positions. Lowering operation will result if the master switch is actuated to one of its lowering positions. If the crane hook i is allowed to travel sufficiently far in the lowering direction to permit limit switch 2%] to reset, the various power circuits are again connected in their normal manner and the crane hook may again be hoisted by actuating the master switch to one of its hoisting positions.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle explained together with the best mode in which it isnow contemplated applying that principle, it will be understood that the apparatus and connections shown and described are merely illustrative, and that the invention is not limited thereto since alterations and modifications will readily occur to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, an electric motor, means providing a shunting circuit for said motor for operation of said motor at slow speed, a brake for said motor having an operating coil in series with said motor, means operable in response to operation of said motor for disconnecting said motor from its source with said shunting circuit intact, and means responsive to disconnection of said motor from said source for interrupting said shunting connection to eifect the setting of said brake.

2. In combination, an electric motor, means providing a shunting circuit for said motor for operation of said motor at slow speed, a brake I for said motor having an operating coil in series with said motor, a limit switch operable in response to operation of said motor for disconnecting said motor from it source with said shunting circuit remaining completed to said source, and means operable in response to the interruption of the armature current of said motor for interrupting said shunting connection to efiect the setting of said brake.

3. In a control system for an electric motor, means providing a shunting circuit for the motor to provide stable operation of said motor at slow speed, a solenoid operated brake for said motor having its solenoid connected in circuit with said motor, a limit switch actuated by operation of said motor for disconnecting said motor from its source with said shunting circuit intact and for completing a dynamic braking circuit for said motor, and means responsive to said operation of said limit switch for interrupting said shunt circuit to efiect deenergization of said solenoid and setting of said brake.

4. In a control system for hoists and the like having an electric hoist motor, the combination with a solenoid brake for said motor having its solenoid in circuit with said motor of a multiposition master switch for controlling the operation of said motor, means operable in at least one position of said master switch for establishing a shunting connection for said motor to provide stable slow speed operation, a limit switch responsive to operation of said motor for disconnecting said motor from its source with said shunting connection established, and a relay operable in said position of said master switch for interrupting said shunting connection to effect deenergization of said solenoid and setting of said brake.

5. A motor control system for hoists and the like having an electric hoist motor comprising in combination, a solenoid brake for said motor having its solenoid in circuit with said motor, a multi-position master switch for controlling the speed of said motor, means operable in a slow speed position of said master switch for establishing a shunting connection for said motor to provide stable slow speed operation of said motor, a limit switch responsive to operation of the hoist for disconnecting the motor from its source with said shunting fect deenergization connection established and said solenoid energized from the source through said shunting connection, said limit switch also establishing a dynamic braking circuit for said motor, and a relay operable in said slow speed position of said master switch and responsive to said operation of said limit switch for interrupting said shunting connection thereby to efof said solenoid and setting of said brake.

6. In a control system for an electric motor, the combination with a solenoid brake for said motor having its solenoid in circuit with said motor of a multi-position master switch having a slow speed position and a high speed position, a contactor operable in said slow speed position of said master switch for establishing a shunting connection for said motor to provide stable slow speed operation of said motor, a limit switch operable in response to operation of said motor for disconnecting said motor from its source with said shunting connection intact, said solenoid being energized from said source through said shunting connection and said brake released, and a relay having its operating coil connected in the armature circuit of said motor and responsive to interruption of current flow in said armature circuit for controlling said contactor to open said shunting connection thereby to deenergize said solenoid and set said brake,

7. A control system for hoists and the like having an electric hoist motor, comprising a solenoid brake for said motor having its solenoid in circuit with said motor, a multi-position reversing type master switch for controlling the direction of rotation and speed of said motor, means operable in a low speed hoisting position of said master switch for establishing a shunting circuit for said motor to provide stable slow speed operation, an overhoist limit switch operable at a predetermined limit of hoist operation for disconnecting said motor from its source, said shunting circuit being intact and said brake solenoid remaining energized through said shunting connection and said brake released, and means responsive to said operation of said limit switch for interrupting said shunting connection thereby to deenergize said solenoid and set said brake.

8. A control system for hoists and the like having an electric hoist motor comprising in combination, a solenoid brake for said motor having its solenoid connected in circuit with said motor, a reversing type master switch for said motor having high and low speed hoisting positions, means operable in said low speed position of said master switch for establishing a shunting circuit for said motor to provide stable slow speed operation of said motor, a limit switch operable in a predetermined position of said hoist for disconnecting said motor from its source, said shunting connection still remaining intact and said solenoid energized through said shunting connection and said brake being released, and a relay responsive to said operation of said limit switch for interrupting said shunt connection to eflect deenergization of said solenoid and setting of said brake, and master switch connections for controlling said relay so that said relay can interrupt'said shunt connection only in said low speed position of said master switch thereby to provide for reestablishing said shunt connection and release of said brake by operation of said master switch to a diilerent position.

JAMES W. 'COOKE. 

